The "standard" or most basic type of control used heretofore for operating electrically-powered wheelchairs has merely comprised a manually-actuated polarity-reversing switch and resistive voltage divider, whether of the incrementally progressive (switched) type or of the continuously variable type (i.e., potentiometer, etc.). The polarity-reversing switch allowed the user to select "forward" or "reverse" movement direction, and the variable resistance component or network selectively changed the voltage effectively applied to the electric drive motor for the wheelchair, thereby changing the speed. Where the wheelchair equipped with such a control encountered a downhill slope, there was always a danger of runaway since the control itself had no built-in protection to prevent such results; that is, the only effective means of braking was to place the control in the "reverse" mode, whereby the forward movement of the vehicle resulting from gravitational forces is opposed by the applied opposite-polarity drive voltage.
Apart from its obvious disadvantages and limitations, the procedure just noted causes substantial power consumption and energy losses in the form of heat, and the control capability or function is inefficient and irregular, being essentially unregulated. Furthermore, the heat losses generated in the resistive components of the control and in the motor are detrimental to these elements and are likely to cause early failure. Many other disadvantages are also involved in such controls, including for example the absence of any assured constant speed at any particular control setting (including especially under the downhill conditions noted above) and arcing and sparking conditions in the control when switched from one polarity to the other, due to the mechanical switching utilized and the reactive components in the control and the motor, whose stored energy jumps across the switch contacts and causes detrimental local heating and burnout. Moreover, the possibility of motor and/or control burnout due to motor stall conditions was always present, since a handicapped person may not be able to avoid such a situation, e.g., one or both wheels may inadvertently become blocked by an obstacle or wedged into a fixed position where the control is set for continuing movement
Improvements and variations on the above-described conventional type of control have been comparatively few and of comparative small magnitude, including for example the use of transistorized switches to reduce the arcing and sparking noted, together with the general concept of pulse-mode operation and pulse-width modulation as a control technique, which provides for more efficient operation as well as a more flexible type of control capability. Nonetheless, many serious problems and disadvantages of the general type discussed above remain present in the typical state-of-the-art controls presently in use.
Accordingly, the need for significantly improved controls having better and safer performance characteristics and increased efficiency has persisted for a considerable length of time. While this is particularly true in the wheelchair-control environment noted above, it is also true with respect to a number of other areas which, while perhaps functionally or operationally remote from the specific area of wheelchairs, nonetheless have very analogous electrical requirements, including for example, many typical switching regulator applications, in which the desired output is the average voltage determined by a selected duty cycle applied to a basic supply voltage.